#include <stdio.h>
void f(char ch[])
{	 	 		 		   	 
    int i;
    for (i = 0; ch[i] != '\0'; i++)           //2
        if (ch[i] == 'a')                     //1
            ch[i] = '*';                      //1
    return ;
}	 	 		 		   	 
int main()
{	 	 		 		   	 
    char c[20];
    printf("input a string:");
    scanf("%s", c);                           //1
    f(c);                                     //1
    printf("string=%s\n", c);                 //1
    return 0;
}	 